Conventional thin film read/write heads in data storage systems generally include an inductive write head in combination with either an inductive or magneto resistive (MR) read head. One type of MR/inductive head includes an inductive write head formed adjacent to a magneto resistive read head. The requirements for higher data density on the magnetic disks have imposed a requirement to read and write more data on narrower tracks located on the disk. Thus, a magnetic head must be of greater precision to maximize its efficiency and sensitivity to read and write data.
Typically, the combined inductive write transducer and MR read transducer are formed from adjacent layers of material on a wafer substrate so as to read and write on the same track. The production of the heads comprises a sequence of deposition and etching steps with the MR transducer formed first, and the inductive write transducer formed on top of the MR transducer. The MR transducer typically comprises a magnetoresistive stripe and two conductors on either side thereof. The stripe height is critical, and is determined by the height defining edge, which is the bottom edge of the stripe. The inductive transducer typically comprises a bottom pole, an insulating layer, half an electrical coil, an insulating layer, a top pole, an insulating layer, and the other half of the coil. The coil halves are interconnected by means of vias, and the coil and the two conductors of the MR transducer are connected to terminals by means of vias. The inductive transducer poles are narrowed to a very narrow pole tip having a precisely controlled width, or throat, the width of which defines the recorded track width. The height of the throat is also an important factor in the optimization of the inductive transducer.
In order to achieve maximum efficiency, both the inductive write transducer and the magnetoresistive read transducer should be designed to have optimum characteristics. A key characteristic for the inductive write transducer is the pole tip height dimension, commonly called throat height. The throat height must be maintained within a limited tolerance for generating an optimum magnetic signal from the input electrical signal. The key characteristic of the magnetoresistive read transducer is the stripe height which must be maintained within a limited tolerance so that the optimum change in resistance is generated in response to the sensed magnetic signal.
Typically, rows of transducers are deposited simultaneously on the wafer substrate using semiconductor type process methods. The wafer substrate may be a hard ceramic material which is used to form disk sliders or tape modules, with the heads deposited thereon. The substrate is then cut into rows of sliders or modules in a side-by-side relationship with the pole tips of the inductive write transducers and the MR stripes of the MR read transducers extending to an edge of the substrate row. The row edge is then lapped to the optimum dimensions of throat height and stripe height.
The accumulated stresses on the substrate and cutting alignment, together with the extremely small dimensions of the heads, may increase the chance that not all the transducers in the row will be precisely aligned with the lapping edge. This condition is defined in the incorporated '868 patent as "row bow". The '868 patent addresses row bow by measuring the resistance of the MR elements in the MR transducers and using the measured resistance to determine the MR transducer stripe height. A lapping control system may use a holder to deflect the substrate row to an appropriate shape to compensate for row bow. Thus, each of the MR transducers in a substrate row of transducers are lapped to the optimum magnetoresistive transducer stripe height based on the measured MR transducer resistances.
The '868 patent assumes that the inductive transducer pole tip throat height is less sensitive and will be within tolerance so long as the MR transducer is within tolerance. Modern higher areal recording densities, however, require the use of higher coercivity disks, which in turn require improved write head element designs and tighter control of the pole tip throat height. Modern electronics may utilize a non-optimum throat height by means of characterization of the throat height and modifying the supplied write signals. Thus, for characterization purposes, it would be of significant benefit to be able to determine throat height before the throat is lapped too far, and is effectively destroyed. Additionally, as the write function becomes more difficult, it will be necessary to bring the throat height to within tolerance while not sacrificing MR transducer performance. It would therefore be beneficial to be able to continue to lap the throat height to bring the throat within tolerance, so long as the MR stripe height is within tolerance, and vice versa.
Additionally, space on the wafer used to form the sliders is extremely important. Any space used for other purposes, such as lapping guides, cannot be used for sliders or nodules, reducing the wafer efficiency and increasing the cost of each slider or module.
The incorporated '547 patent illustrates two separate types of single electrical lapping guides (ELG) positioned in the kerfs between sliders in a substrate row. One type of ELG is a switch that is provided at two separate lengths. The second type of ELG is a resistive device, also provided at two separate lengths. The resistive devices may provide the fine lapping control for the pole tip throat height of inductive transducers and may be calibrated by the two switches as described in the '547 patent.
The '547 patent assumes that positioning the lapping guides across the row in separate kerfs provides adequate throat height lapping control. The '547 patent does not consider MR stripe height.
However, the distortion of a wafer row caused by row bow and the need for more accurate control of MR stripe height and pole tip throat height may require that the lapping guides be as close to the associated individual sliders or modules as possible.
Furthermore, it is desirable to predict both stripe height and throat height to control the lapping of either the inductive transducer or the MR transducer, or both, and the means provided should not occupy space that otherwise may be used for forming sliders or modules.